This invention relates to a process for producing alkenyl aromatic compounds. More particularly, it relates to a process for cleaving certain diphenyl alkanes, and an improved catalyst therefor.
It is well-known that dihydroxy diphenyl alkanes can be cleaved by heating them in the presence of an alkaline catalyst to give phenol and alkenyl phenols, and several methods have been proposed for this cleavage reaction. For example, U.K. Pat. No. 905,994 teaches the use of basic catalysts such as alkali metals or alkaline earth metals or the oxides, hydroxides, alcoholates, phenolates, alkyl-carboxylates, carbonates, amides and hydrides thereof, as well as aluminum, zinc, cadmium and lead, or the above-mentioned compounds of these metals in a process for the production of alpha-alkenyl, alpha-cycloalkenyl and alpha-aralkenyl phenols. Other known methods for the preparation of alpha-alkenyl phenols are disclosed in U.S. Pat. No. 4,054,611; U.S. Pat. No. 4,242,528; U.S. Pat. No. 4,245,128; U.S. Pat. No. 2,497,503; and U.S. Pat No. 1,798,813. The latter patent discloses that compounds such as 4-isopropylene phenol can be prepared by thermally cleaving dihydroxydiaryl alkanes in the presence of a surface catalyst, such as magnesium aluminum hydrosilicates, fuller's earth, silica gel, active carbon and similar porous bodies. However, the majority of said patents employ simple catalysts such as sodium hydroxide, potassium hydroxide, or the alkali metal salts of bisphenol A. Scuh catalysts are disadvantageous in that they produce relatively large amounts of polymers and tars which reduce the yield of the desired compounds.
U.S. Pat. No. 3,576,891 discloses a supported alkali metal hydroxide catalyst for the removal of esters and acids from t-butyl alcohol. It is taught that the alkali metal hydroxide is supported on an inert support such as magnesia. The final catalyst composition is taught to contain from about 5 weight percent to 30 weight percent alkali metal hydroxide.
U.S. Pat. No. 4,450,310 discloses catalysts comprising the mixed oxide of alkali metal and alkaline earth metals. Said catalysts are prepared by calcination in air of compounds of said metals, examples of suitable ions being carbonates, hydroxides, halides or salts of organic or inorganic acids. Said patent discloses the use of these catalysts for the conversion of methane to olefins and hydrogen. Said catalysts may optionally contain promoters such as rhodium, copper, rhenium, tungsten, zirconium, and mixtures thereof. The preparation of said catalysts is disadvantageous in that calcination at very high temperatures is required.
In view of the deficiencies of the prior art, it would be desirable to have a supported catalyst having a small percentage of alkali metal, which could be easily prepared, and which could be employed advantageously for the cleavage of dihydroxydiaryl alkanes.